Japanese Patent No. 3,606,164 (corresponding to U.S. Pat. No. 6,473,290, hereinafter referred to as the patent document 1) describes an angular velocity sensor that includes a substrate, a movable unit coupled with the substrate through a supporting beam, a comb-shaped movable electrode provided in the movable unit, and a comb-shaped fixed electrode provided in the substrate. The movable unit serves as a vibrator. The movable unit is supported via the supporting beam, and is displaceable in a detecting direction. The comb-shaped fixed electrode includes a plurality of fixed electrode portions arranged in the detecting direction at predetermined intervals. The comb-shaped movable electrode includes a plurality of movable electrode portions. The movable electrode is engaged with the fixed electrode such that each of the movable electrode portions is located between adjacent two of the fixed electrode portions.
The angular velocity sensor detects an angular velocity by detecting a change in capacitance of a capacitor provided by the fixed electrode portions and the movable electrode portions when the movable unit is displaced in the detecting direction due to Coriolis force along the detecting direction.
Japanese Patent No. 3,512,004 (hereinafter referred to as the patent document 2) describes an angular velocity sensor that includes a substrate, a vibrator, a servo electrode, and a servo control circuit. The vibrator is coupled with the substrate through a beam and a frame. The vibrator is displaceable in a vibrating direction and a detecting direction. The vibrating direction and the detecting direction are parallel to a surface of the substrate and perpendicular to each other. The servo electrode and the servo control circuit restrict vibration of the vibrator in the detecting direction. The angular velocity sensor calculates a servo voltage for restricting the vibration of the vibrator in the detecting direction, and calculates an angular velocity based on the servo voltage.
Each of the above-described angular velocity sensors is manufactured by processing a silicon-on-insulator (SOI) substrate by a known micromachining technique. In such processing, machining error occurs in some measure. If machining error occurs, the vibration in the vibrating direction may escape in the detecting direction. Further, in a case where the vibrator is vibrated under atmospheric pressure or under pressure approximate to the atmospheric pressure, the vibration in the vibrating direction may escape in the detecting direction due to viscosity of gas molecules. As a result, the vibrator vibrates in the detecting direction due to the Coriolis force, an escaping component caused by the machining error, and an escaping component caused by the viscosity of gas molecules.
The angular velocity sensor described in the patent document 1 does not have a configuration for restricting influence of the error-caused escaping component and the viscosity-caused escaping component. Thus, detection accuracy of the angular velocity may be reduced by the escaping components.
In the angular velocity sensor described in the patent document 2, the servo electrode and the servo control circuit restrict vibration of the vibrator in the detecting direction. Thus, influence of the error-caused escaping component and the viscosity-caused escaping component may be reduced.
As described above, however, the vibrator vibrates in the detecting direction due to the Coriolis force, the error-caused escaping component and the viscosity-caused escaping component. Therefore, if the escaping components increase, a servo load applied to the servo electrode and the servo control circuit may increase.